Pressure balanced fluid control device

ABSTRACT

The present invention is directed to a pressure balanced fluid control device. In one illustrative embodiment, the device comprises a body, a bonnet coupled to the body, a valve stem operatively coupled to a gate positioned in the body, a valve stem seal positioned between the valve stem and the bonnet, wherein a sealed cavity exists above the valve stem seal, and an opening through the bonnet that is adapted to allow a pressure of a working fluid flowing through the valve to be exerted in the sealed cavity above the valve stem seal. In another illustrative embodiment, the device comprises a body, a bonnet coupled to the body, a valve stem operatively coupled to a gate positioned in the body, a valve stem seal positioned between the valve stem and the bonnet, wherein a sealed cavity exists above the valve stem seal, and an opening through the bonnet, the opening being in fluid communication with the sealed cavity and an interior region of the body. In a further illustrative embodiment, the device comprises a body, a bonnet coupled to the body, a valve stem operatively coupled to a gate positioned in the body, a valve stem seal positioned between the valve stem and the bonnet, wherein a sealed cavity exists above the valve stem seal, a piston chamber formed in the bonnet, the piston chamber being in fluid communication with the sealed cavity and an interior region of the body, and a piston positioned in the piston chamber.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is generally related to the field of pressurecontrol devices, and, in one particular example, to a pressure balancedfluid control device.

2. Description of the Related Art

Fluid control devices, such as gate valves, are commonly employed in avariety of different industries, e.g., surface and subsea oil and gasdrilling and producing industries. Gate valves may be classified aseither balanced stem or unbalanced stem valves. As is well known in theart, in an unbalanced stem gate valve, there is a net force exerted onthe valve stem. In some cases, this force may be equal to the pressureexerted within the valve body multiplied by the seal area of the stem.In unbalanced gate valve designs, it is often necessary to limit thestem seal area to reduce the unbalanced stem force and thus theoperating torque required to actuate the gate valve. Although reducingthe stem seal area may reduce unbalanced forces, such a limitation mayplace a number of undesirable constraints on the design of a gate valve.

In some embodiments, particularly surface valves, balanced stem gatevalves include a second stem attached to the opposite end of the gatewherein the second stem has essentially the same seal area as the valvestem. Accordingly, there is no net force acting on the valve stem. Onedrawback to the use of such a balanced stem design is that the secondstem increases the size, cost and complexity of the valve, andintroduces additional potential leak paths. For example, in many subseaapplications, there is no available space for incorporating a balancestem into the design of the subsea equipment, e.g., a Christmas tree.

FIG. 1 depicts one illustrative embodiment of a prior art balanced stemgate valve 10. In general, the gate valve 10 is comprised of a body 12,a bonnet 14, a gate 16 having an opening 18 formed therethrough, and aseal 15, e.g., typically a metal gasket. The gate valve 10 furthercomprises a plurality of flanges 29 and it has an opening 31 formedtherethrough to allow working fluid to pass through the gate valve 10when the gate 16 is positioned such that the opening 18 in the gate 16is aligned with the opening 31 through the body 12. The bonnet 14 issecured to the body 12 by a plurality of nuts and studs, generallyindicated by the reference number 14 a. The gate valve 10 furtherincludes a valve stem 20 and a pressure balance stem 22. The valve stem20 is coupled to the gate 16 by a lifting nut 21. A pin 21A couples thelifting nut 21 to the stem 20 such that there is no rotation betweenthese components. A directional valve stem seal 11, e.g., UV elastomerpacking, is positioned in the bonnet 14 around the valve stem 20. Thepressure balance stem 22 is positioned within a balance stem housing 22a that is coupled to the body 12 by a plurality of studs and nuts,generally indicated by the reference number 22 b. A directional seal 13is positioned around the pressure balance stem 22.

The gate valve 10 further comprises means for actuating the gate 16. Inthe depicted embodiment, the valve 10 employs a roller screw assembly 24and an actuator handle assembly 28. Hydraulic or electrical actuatorscan also be employed with the valve 10 if desired. The roller screwassembly 24 is partially positioned within a bonnet cap 26 that isthreadingly coupled to the bonnet 14 at a threaded connection 27. Aplurality of set screws 37 are used to further secure the bonnet cap 26to the bonnet 14 after the threaded connection 27 is made. The rollerscrew assembly 24 further comprises a roller screw 30, a threaded nut32, a roller screw housing 25, a plurality of bearings 36 and a key 34.The key 34 couples the roller screw nut 32 to the roller screw housing25. An elastomer seal 40 is provided between the bonnet cap 26 and theroller screw housing 25. An elastomer seal 41 is positioned between thebonnet 14 and the bonnet cap 26. Also depicted in FIG. 1 are a pluralityof openings 42 having threaded fasteners 43, e.g., screws, positionedtherein. The openings 42 are provided as a means of providing lubricantto the bearings 36. In some cases, e.g., sub-surface applications, suchopenings would not typically be present. The valve stem 20 isthreadingly coupled to the roller screw 30 via a threaded connection 33(external threads on an end of the valve stem 20 engage an internallythreaded opening formed in the roller screw 30). The valve stem 20 mayfurther be coupled to the roller screw 30 by a pin 23.

Historically, gate valves have required a relatively large amount oftorque to actuate the valve, e.g., actuation systems involving theengagement of high friction ACME threads. However, such high torqueactuation systems present several problems. For example, with respect tomanually actuated valves, such high torque valves required thegeneration of relatively large forces, thus making actuating such gatevalves difficult and very time-consuming given that the actuating forcewas generated by an operator attempting to manually open or close thegate valve. Even in valves employing electrical or hydraulic actuators,the relatively large torque required to actuate the valve required thatthe actuator components be relatively large so that they could readilygenerate the necessary torque to actuate the gate valve in a timelymanner.

However, in recent years, efforts have been made to reduce the torquerequired to actuate a gate valve. Such reduced torque is desirablebecause it requires less force to actuate the valve, e.g., the reductionin torque enables the use of smaller, less expensive actuators.Moreover, use of smaller actuators, e.g., electrical or hydraulicmotors, is desirable in many applications in which there is limitedspace availability for such components. Unfortunately, problems mayarise when using a relatively low torque actuating assembly, e.g., aroller screw assembly in an unbalanced gate valve. Due to the lowfriction and operating torque of the roller screw assembly, unbalancedstem forces may be sufficient to “back-drive” the roller screw 30 andthereby raise the gate 16. Of course, such a situation is undesirablefrom an operational point of view. Thus, when employing reduced forceactuating assemblies, such as a roller screw assembly, it is usuallynecessary to employ a pressure balancing technique or device, e.g., asecond pressure balancing stem, in an effort to avoid the “back-drive”situation described above. However, in addition to adding cost andcomplexity to a valve design, there are many applications where there islimited spaced available. Thus, the use of the pressure balanced stem 22is undesirable in such a situation.

The present invention is directed to an apparatus and methods forsolving, or at least reducing the effects of, some or all of theaforementioned problems.

SUMMARY OF THE INVENTION

The present invention is directed to a pressure balanced fluid controldevice. In one illustrative embodiment, the device comprises a body, avalve stem operatively coupled to a gate positioned in the body, a valvestem seal positioned around the valve stem, wherein a sealed cavityexists above the valve stem seal, and an opening in fluid communicationwith the sealed cavity and an interior region of the body, the openingallowing a pressure of the working fluid to be exerted in the sealedcavity above the valve stem seal.

In another illustrative embodiment, the device comprises a body, abonnet coupled to the body, a valve stem operatively coupled to a gatepositioned in the body, a valve stem seal positioned between the valvestem and the bonnet, wherein a sealed cavity exists above the valve stemseal, and an opening through the bonnet that is adapted to allow apressure of a working fluid flowing through the valve to be exerted inthe sealed cavity above the valve stem seal.

In yet another illustrative embodiment, the device comprises a body, avalve stem operatively coupled to a gate positioned in the body, a valvestem seal positioned around the valve stem, wherein a sealed cavityexists above the valve stem seal, and an opening through the body thatallows a pressure of the working fluid to be exerted in the sealedcavity above the valve stem seal.

In another illustrative embodiment, the device comprises a body, abonnet coupled to the body, a valve stem operatively coupled to a gatepositioned in the body, a valve stem seal positioned between the valvestem and the bonnet, wherein a sealed cavity exists above the valve stemseal, and an opening through the bonnet, the opening being in fluidcommunication with the sealed cavity and an interior region of the body.

In yet another illustrative embodiment, the device comprises a body, abonnet coupled to the body, a valve stem operatively coupled to a gatepositioned in the body, a valve stem seal positioned between the valvestem and the bonnet, wherein a sealed cavity exists above the valve stemseal, and an opening through the bonnet that is adapted to allow aworking fluid flowing through the valve to enter the sealed cavity,thereby exerting a pressure of the working fluid in the sealed cavityabove the valve stem seal.

In still another illustrative embodiment, the device comprises a body, abonnet coupled to the body, a valve stem operatively coupled to a gatepositioned in the body, a bonnet cap coupled to the bonnet, a rollerscrew assembly operatively coupled to the valve stem, the roller screwassembly comprising a housing, a portion of which extends through thebonnet cap, a first valve stem seal positioned between the valve stemand the bonnet, a second seal positioned between the bonnet cap and thebonnet, and a third seal positioned between the bonnet cap and thehousing, wherein a sealed cavity exists above the first valve stem seal,the sealed cavity being defined by a portion of the bonnet cap, thefirst valve stem seal, the second seal and the third seal, and anopening through the bonnet that is adapted to allow a working fluidflowing through the device to enter the sealed cavity, thereby exertinga pressure of the working fluid in the sealed cavity above the valvestem seal.

In a further illustrative embodiment, the device comprises a body, avalve stem operatively coupled to a gate positioned in the body, a valvestem seal positioned around the valve stem, wherein a sealed cavityexists above the valve stem seal, a piston chamber, the piston chamberbeing in fluid communication with the sealed cavity and an interiorregion of the body, and a piston positioned in the piston chamber.

In yet a further illustrative embodiment, the device comprises a body, abonnet coupled to the body, a valve stem operatively coupled to a gatepositioned in the body, a valve stem seal positioned between the valvestem and the bonnet, wherein a sealed cavity exists above the valve stemseal, a piston chamber formed in the bonnet, the piston chamber being influid communication with the sealed cavity and an interior region of thebody, and a piston positioned in the piston chamber.

In yet a further illustrative embodiment, the device comprises a body, abonnet coupled to the body, a valve stem operatively coupled to a gatepositioned in the body, a bonnet cap coupled to the bonnet, a rollerscrew assembly operatively coupled to the valve stem, the roller screwassembly comprising a housing, a portion of which extends through thebonnet cap, a first valve stem seal positioned between the valve stemand the bonnet, a second seal positioned between the bonnet cap and thebonnet, and a third seal positioned between the bonnet cap and thehousing, wherein a sealed cavity exists above the first valve stem seal,the sealed cavity being defined by a portion of the bonnet cap, thefirst valve stem seal, the second seal and the third seal, a pistonchamber formed in the bonnet, the piston chamber being in fluidcommunication with the sealed cavity and an interior region of the body,and a piston positioned in the piston chamber.

In still a further illustrative embodiment, the device comprises a body,a bonnet coupled to the body, a valve stem operatively coupled to a gatepositioned in the body, a valve stem seal positioned between the valvestem and the bonnet, wherein a sealed cavity exists above the valve stemseal, and means for allowing a pressure of a working fluid flowingthrough the valve to be exerted in the sealed cavity while preventingthe working fluid from entering the sealed cavity.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be understood by reference to the followingdescription taken in conjunction with the accompanying drawings, inwhich like reference numerals identify like elements, and in which:

FIG. 1 is a cross-sectional view of an illustrative balanced stem gatevalve design;

FIG. 2 is a cross-sectional view of one illustrative embodiment of thepresent invention; and

FIGS. 3A-3C are cross-sectional views of a gate valve in accordance withanother illustrative embodiment of the present invention.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and are herein described in detail. It shouldbe understood, however, that the description herein of specificembodiments is not intended to limit the invention to the particularforms disclosed, but on the contrary, the intention is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

Illustrative embodiments of the invention are described below. In theinterest of clarity, not all features of an actual implementation aredescribed in this specification. It will of course be appreciated thatin the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure.

The present invention will now be described with reference to theattached figures. The words and phrases used herein should be understoodand interpreted to have a meaning consistent with the understanding ofthose words and phrases by those skilled in the relevant art. No specialdefinition of a term or phrase, i.e., a definition that is differentfrom the ordinary and customary meaning as understood by those skilledin the art, is intended to be implied by consistent usage of the term orphrase herein. To the extent that a term or phrase is intended to have aspecial meaning, i.e., a meaning other than that understood by skilledartisans, such a special definition will be expressly set forth in thespecification in a definitional manner that directly and unequivocallyprovides the special definition for the term or phrase.

In general, the present invention is directed to a pressure balancedfluid control device. As will be recognized by those skilled in the artafter a complete reading of the present application, the presentinvention may be employed with a variety of different devices and with avariety of different applications. For example, the illustrative valvedescribed herein may be used in subsea or surface applications, e.g.,subsea or surface wellhead or production facilities related to oil andgas production. Thus, the present invention should not be considered aslimited to any particular type of fluid control device or to theintended use or function of such a device unless such limitations areexpressly set forth in the appended claims. For ease of reference, inFIGS. 2 and 3A-3C, the same reference number will be employed toidentify components of the valve that have been previously describedwith respect to FIG. 1. Thus, the description set forth above withrespect to FIG. 1 may be applicable to the other figures set forth inthe application.

FIG. 2 depicts one illustrative embodiment of a valve 100 where thepresent invention may be employed in a subsea application. As showntherein, the body 12A may be a portion of another structure, e.g., aChristmas tree, a tubing head, a wellhead, etc. The body 12A is intendedto be representative in nature as the body 12A may be of any generalshape or configuration, and it may be part of a larger structure, e.g.,a piece of subsea equipment. The body 12A may also be a separatestructure that is intended to only house the valve 100.

The opening 31 may one of many openings formed in a portion of the body12. The opening 31 may also be the primary opening in the structure,i.e., the main bore extending through the subsea equipment, or it may bean ancillary flow path created within the subsea body. In any event, thegate 16 of the valve 100 may be used to regulate the flow of a workingfluid through the opening 31. In one illustrative embodiment, asdepicted in the drawings, an opening 102 is formed through the bonnet14. The valve 100 further comprises a directional seal pack 103 betweenthe bonnet cap 26 and the roller screw housing 25, a directional sealpack 104 between the bonnet cap 26 and the bonnet 14, and abi-directional valve stem seal 106 between the bonnet 14 and the valvestem 20. The structure and composition of such directional andbi-directional seals are well known to those skilled in the art. Aretaining ring 108 and locking nut 110 are used to retain thedirectional seal 103 in place. The bonnet cap 26 and the seals 103, 104,106 define a sealed cavity 112, i.e., in all interior spaces within thearea defined by the bonnet cap 26 and the seals 103, 104 and 106. In thedepicted embodiment, the bonnet 14 is a separate component that may becoupled to the valve body 12A. However, after a complete reading of thepresent application, those skilled in the art will appreciate that thebonnet 14 may be a separate component or formed integral with the body12A depending on the particular embodiment. Thus, the present inventionshould not be considered as limited to any particular embodiment or typeof bonnet/body configuration unless such limitations are expresslyrecited in the appended claims.

Also depicted in FIG. 2 is a schematically depicted arm 111 of a remoteoperated vehicle (ROV) that may be used to actuate the illustrativevalve depicted in FIG. 2. Such ROV vehicles and their use are well knownin the art. In the depicted embodiment, the ROV arm 111 may be used tocreate a rotational force to actuate the valve 100 through use of theroller screw assembly 24. However, the present invention may be used insituations where other means are employed to actuate the valve, e.g.,electric or hydraulic motors, manual actuation, etc. Moreover, althoughthe valve 100 depicted herein is actuated by application of a rotationalforce to the roller screw assembly 24, the present invention may be usedin applications where the valve is actuated by a push-pull mechanism,i.e., translational movement. In such an application, the ROV arm 111may be used to push or pull on a component operatively coupled to thevalve stem 20 to achieve the desired results. Thus, the presentinvention should not be considered as limited to the manner in which thevalve is actuated or the means used to actuate the valve, unless suchlimitations are expressly set forth in the appended claims.

In the depicted embodiment, the opening 102 is in fluid communicationwith the sealed cavity 112, as well as the interior region of the body12A. In one embodiment, the opening 102 is provided in the bonnet 14such that the internal pressure existing within the body 12A, e.g.,within the opening 31, may also exist within the sealed cavity 112 asdefined by the bonnet cap 26, and the seals 103, 104 and 106. That is,the opening 102 is provided such that the pressure above the valve stemseal 106 is the same as the pressure within the body 12A of the valve100, i.e., the working pressure (“WP” ) of the working fluid flowingthrough the opening 31 exists on both sides of the valve stem seal 106.In other embodiments, the opening 102 may extend entirely or at leastpartially through the body 12A such that pressure of the working fluidmay be exerted on both sides of the valve stem seal 106, i.e., theopening 102 may not extend through the bonnet 14. In some cases, theopening 102 may be coupled to a conduit that extends between the openingformed in the body 12A and the sealed cavity 112.

In one illustrative embodiment, the opening 102 allows working fluidflowing through the valve 100 to enter into the sealed cavity 112. Inthis embodiment, there is no seal between the inlet 105 of the opening102 and the sealed cavity 112 to prevent the flow of working fluid intothe sealed cavity 112. By allowing the working fluid to enter the sealedcavity 112, the pressure on opposite sides of the valve stem seal 106 isequal, thereby balancing the pressure forces acting on the valve stem20.

The size and configuration of the opening 102, as well as its positionwithin the bonnet 14 and/or body 12A, may vary depending upon theparticular application. In one illustrative embodiment, the opening 102is positioned in the bonnet 14 and it has a diameter of approximately1/16-⅛ inch. In general, the smaller the opening 102, the less likelyparticulate matter can traverse into the sealed cavity 112 and damageother components, e.g., the roller screw assembly 24. Of course, thecomponents of the valve 100 that will be subjected to the fluid workingpressure within the sealed cavity 112 will need to be designed towithstand such a working pressure. In the field of oil and gasproduction, the working pressure may be relatively high, e.g., on theorder of 5,000-15,000 psi. For example, depending upon the application,the wall thickness of the bonnet cap 26 may need to be increasedrelative to bonnet caps not subjected to the working pressure of theworking fluid.

FIGS. 3A-3C depict yet another illustrative embodiment of a valve 100 inaccordance with the present invention. As shown therein, the valve 100comprises a piston 130 positioned in a piston chamber 132. In thedepicted embodiment, the piston chamber 132 is formed in the bonnet 14.In some applications, the piston chamber 132 may be formed at somelocation within the body 12A. A filter 140 may also provided. A seal134, e.g., an elastomer O-ring, is positioned around the piston 130 toprovide sealing engagement between the piston 130 and the surface 133 ofthe piston chamber 132. The piston 130 is secured within the pistonchamber 132 by a piston retainer 136 that is threadingly coupled to theinterior of the piston chamber 132. That is, the piston retainer 136 isexternally threaded while a portion of the interior of the pistonchamber 132 is internally threaded. An opening 137 is provided in thepiston retainer 136 to allow working fluid within the valve 100 tocontact the piston 130. The piston chamber 132 is in fluid communicationwith the sealed cavity 112 (via the opening 102) and with the interiorof the body 12. The size, location and configuration of the pistonchamber 132 and the piston 130 may vary depending upon the particularapplication. In the illustrative embodiment depicted in FIGS. 3A-3C, thepiston 130 and the piston chamber 132 have a generally circularcross-sectional configuration. In one illustrative embodiment, thepiston 130 has a diameter of approximately 0.5-1.5 inches, and thepiston chamber 132 has a depth of approximately 3-4 inches. The volumeof the piston chamber 132 is sized to compensate for the contractionand/or expansion of the sealed cavity volume and the fluid in the sealedcavity 112 due to a variety of factors, such as external forces,temperature, air in the cavity 112, etc. The volume of the pistonchamber 132 may vary depending upon the particular application.

If employed, the filter 140 may be positioned upstream or on the workingfluid side of the piston 130 within the piston retainer 136 and securedtherein by filter support housing 142. The filter support housing 142 isthreadingly coupled to the piston retainer 136, i.e., the filter supporthousing 142 is externally threaded while a portion of the interior ofthe piston retainer 136 is internally threaded. The filter 140 may notbe needed in all applications. When employed, the filter 140 acts as anadditional safeguard to prevent particulate matter from entering thesealed cavity 112. When employed, the filter 140 may be of any size,configuration and material sufficient to perform the filtering actionsdescribed herein. In one illustrative embodiment, the filter 140 is astainless steel mesh having an aperture size of approximately 0.057″ anda nominal open area of approximately 55%. Although not depicted in FIG.2, a filter may also be employed in the embodiment of the valve 100depicted therein to filter the working fluid flowing through the opening102. For example, a filter may be positioned over the opening 102 in arecess formed in the bonnet 14 and secured therein by a structuresimilar to the filter support housing 142.

A check valve 150 (see FIG. 3A) is provided in the bonnet cap 26. Thecheck valve 150 allows the sealed cavity 112 and all spaces above thepiston 130 to be filled with a lubricant fluid or a hydraulic fluid forlubrication. By using the piston 130 depicted in FIGS. 3A-3C, theinternal working pressure within the valve 100 may be transmittedthroughout the sealed cavity 112 while separating the working fluid, andthe possible contaminants therein, from the sealed cavity 112 andcomponents contained therein, e.g., the roller screw assembly 24.

FIGS. 3B and 3C are provided to depict an illustrative example of thesituation where the piston 130 is subjected to working pressure of theworking fluid flowing through the valve 100. FIG. 3B depicts thesituation where the sealed cavity 112 has been filled with a lubricantfluid or a hydraulic fluid through the check valve 150. The hydraulicfluid is present in all open spaces throughout the sealed cavity 112,the opening 102 and the piston chamber 132 above the top surface 130 aof the piston 130. At the point in time depicted in FIG. 3B, there is nointernal pressure within the body 12. FIG. 3C depicts the piston 130 ata point where a working fluid is flowing through the valve 100 at aworking pressure (“WP”). The piston 130 is exposed to the working fluidvia the opening 137 in the piston retainer 136. As can be seen in FIG.3C, the piston 130 has moved upward within the piston chamber 132 andthe pressure above and below the piston 130 is equal to the workingpressure (WP) of the working fluid flowing through the valve 100. Thepiston 130 may or may not move when subjected to the working pressure ofthe working fluid. Typically, there will be some movement due to theexistence of very small air pockets within the sealed cavity 112,expansion of some of the components that define the sealed cavity 112,e.g., the bonnet cap 26, etc. In general, the movement of the piston 130should be relatively minimal.

Through use of the present invention depicted in FIGS. 3A-3C, theworking pressure (“WP”) of the working fluid flowing through the valve100 is transmitted to the sealed cavity 112 while effectively isolatingthe working fluid from the cavity 112 itself. Ultimately, by equalizingthe pressure on both sides of the valve stem seal 106, the stem 20 isbalanced and there is no net force acting on the roller screw assembly24 that will tend to undesirably “back-drive” the roller screw 30. As aresult of the novel inventions provided herein, a balanced stem valve100 is provided without the need of providing an offsetting balancestem. In turn, the valve 100 of the present invention is more compactand may be employed in situations where space availability is limited.

As will be recognized by those skilled in the art after a completereading of the present application, the components of the valvesdescribed herein may be manufactured from a variety of materialscommonly found in traditional valves, e.g., carbon steel, stainlesssteel, etc. Moreover, the valve 100 described herein may be oriented inany desired direction, e.g., where the valve stem 20 is disposedvertically, horizontally or at any other angle.

The present invention is directed to a pressure balanced fluid controldevice. In one illustrative embodiment, the device comprises a body, avalve stem operatively coupled to a gate positioned in the body, a valvestem seal positioned around the valve stem, wherein a sealed cavityexists above the valve stem seal, and an opening in fluid communicationwith the sealed cavity and an interior region of the body, the openingallowing a pressure of the working fluid to be exerted in the sealedcavity above the valve stem seal.

In another illustrative embodiment, the device comprises a body, abonnet coupled to the body, a valve stem operatively coupled to a gatepositioned in the body, a valve stem seal positioned between the valvestem and the bonnet, wherein a sealed cavity exists above the valve stemseal, and an opening through the bonnet that is adapted to allow apressure of a working fluid flowing through the valve to be exerted inthe sealed cavity above the valve stem seal.

In yet another illustrative embodiment, the device comprises a body, avalve stem operatively coupled to a gate positioned in the body, a valvestem seal positioned around the valve stem, wherein a sealed cavityexists above the valve stem seal, and an opening through the body thatallows a pressure of the working fluid to be exerted in the sealedcavity above the valve stem seal.

In another illustrative embodiment, the device comprises a body, abonnet coupled to the body, a valve stem operatively coupled to a gatepositioned in the body, a valve stem seal positioned between the valvestem and the bonnet, wherein a sealed cavity exists above the valve stemseal, and an opening through the bonnet, the opening being in fluidcommunication with the sealed cavity and an interior region of the body.

In yet another illustrative embodiment, the device comprises a body, abonnet coupled to the body, a valve stem operatively coupled to a gatepositioned in the body, a valve stem seal positioned between the valvestem and the bonnet, wherein a sealed cavity exists above the valve stemseal, and an opening through the bonnet that is adapted to allow aworking fluid flowing through the valve to enter the sealed cavity,thereby exerting a pressure of the working fluid in the sealed cavityabove the valve stem seal.

In still another illustrative embodiment, the device comprises a body, abonnet coupled to the body, a valve stem operatively coupled to a gatepositioned in the body, a bonnet cap coupled to the bonnet, a rollerscrew assembly operatively coupled to the valve stem, the roller screwassembly comprising a housing, a portion of which extends through thebonnet cap, a first valve stem seal positioned between the valve stemand the bonnet, a second seal positioned between the bonnet cap and thebonnet, and a third seal positioned between the bonnet cap and thehousing, wherein a sealed cavity exists above the first valve stem seal,the sealed cavity being defined by a portion of the bonnet cap, thefirst valve stem seal, the second seal and the third seal, and anopening through the bonnet that is adapted to allow a working fluidflowing through the device to enter the sealed cavity, thereby exertinga pressure of the working fluid in the sealed cavity above the valvestem seal.

In a further illustrative embodiment, the device comprises a body, avalve stem operatively coupled to a gate positioned in the body, a valvestem seal positioned around the valve stem, wherein a sealed cavityexists above the valve stem seal, a piston chamber, the piston chamberbeing in fluid communication with the sealed cavity and an interiorregion of the body, and a piston positioned in the piston chamber.

In yet a further illustrative embodiment, the device comprises a body, abonnet coupled to the body, a valve stem operatively coupled to a gatepositioned in the body, a valve stem seal positioned between the valvestem and the bonnet, wherein a sealed cavity exists above the valve stemseal, a piston chamber formed in the bonnet, the piston chamber being influid communication with the sealed cavity and an interior region of thebody, and a piston positioned in the piston chamber.

In yet a further illustrative embodiment, the device comprises a body, abonnet coupled to the body, a valve stem operatively coupled to a gatepositioned in the body, a bonnet cap coupled to the bonnet, a rollerscrew assembly operatively coupled to the valve stem, the roller screwassembly comprising a housing, a portion of which extends through thebonnet cap, a first valve stem seal positioned between the valve stemand the bonnet, a second seal positioned between the bonnet cap and thebonnet, and a third seal positioned between the bonnet cap and thehousing, wherein a sealed cavity exists above the first valve stem seal,the sealed cavity being defined by a portion of the bonnet cap, thefirst valve stem seal, the second seal and the third seal, a pistonchamber formed in the bonnet, the piston chamber being in fluidcommunication with the sealed cavity and an interior region of the body,and a piston positioned in the piston chamber.

In still a further illustrative embodiment, the device comprises a body,a bonnet coupled to the body, a valve stem operatively coupled to a gatepositioned in the body, a valve stem seal positioned between the valvestem and the bonnet, wherein a sealed cavity exists above the valve stemseal, and means for allowing a pressure of a working fluid flowingthrough the valve to be exerted in the sealed cavity while preventingthe working fluid from entering the sealed cavity.

The particular embodiments disclosed above are illustrative only, as theinvention may be modified and practiced in different but equivalentmanners apparent to those skilled in the art having the benefit of theteachings herein. For example, the process steps set forth above may beperformed in a different order. Furthermore, no limitations are intendedto the details of construction or design herein shown, other than asdescribed in the claims below. It is therefore evident that theparticular embodiments disclosed above may be altered or modified andall such variations are considered within the scope and spirit of theinvention. Accordingly, the protection sought herein is as set forth inthe claims below.

1.-30. (canceled)
 31. A device, comprising: a body; a valve stemoperatively coupled to a gate positioned in said body; a valve stem sealpositioned around said valve stem, wherein a sealed cavity exists abovesaid valve stem seal; a piston chamber, said piston chamber being influid communication with said sealed cavity and an interior region ofsaid body; and a piston positioned in said piston chamber.
 32. Thedevice of claim 31, wherein said piston chamber is formed in a bonnetthat is coupled to said body.
 33. The device of claim 31, wherein saidpiston chamber is formed in a portion of said body.
 34. The device ofclaim 31, wherein said valve stem is operatively coupled to a rollerscrew.
 35. The device of claim 31, further comprising a piston retainingring that is adapted to retain said piston in said piston chamber. 36.The device of claim 35, further comprising a filter positioned betweensaid piston and said interior region of said body.
 37. The device ofclaim 35, further comprising: a filter positioned between said pistonand said interior region of said body; and a filter support ring toretain said filter in position, said filter support ring beingthreadingly coupled to said piston retaining ring.
 38. The device ofclaim 31, wherein said valve stem seal is a bi-directional seal.
 39. Thedevice of claim 31, wherein said sealed cavity is at least partiallydefined by a bonnet cap.
 40. The device of claim 31, further comprisinga seal positioned between said piston and said piston chamber.
 41. Thedevice of claim 31, further comprising a hydraulic fluid positioned insaid sealed cavity above said piston, wherein said hydraulic fluid isadapted to be substantially isolated from said working fluid by saidpiston.
 42. A device, comprising: a body; a bonnet coupled to said body;a valve stem operatively coupled to a gate positioned in said body; avalve stem seal positioned between said valve stem and said bonnet,wherein a sealed cavity exists above said valve stem seal; a pistonchamber formed in said bonnet, said piston chamber being in fluidcommunication with said sealed cavity and an interior region of saidbody; and a piston positioned in said piston chamber.
 43. The device ofclaim 42, wherein said valve stem is operatively coupled to a rollerscrew.
 44. The device of claim 42, further comprising a piston retainingring that is threadingly coupled to said bonnet, said piston retainingring being adapted to retain said piston in said piston chamber.
 45. Thedevice of claim 44, further comprising a filter positioned in saidbonnet between said piston and said interior region of said body. 46.The device of claim 44, further comprising: a filter positioned in saidbonnet between said piston and said interior region of said body; and afilter support ring to retain said filter in position, said filtersupport ring being threadingly coupled to said piston retaining ring.47. The device of claim 42, wherein said valve stem seal is abi-directional seal.
 48. The device of claim 42, wherein said sealedcavity is at least partially defined by a bonnet cap that is coupled tosaid bonnet.
 49. The device of claim 42, wherein said sealed cavity isat least partially defined by a bonnet cap that is coupled to saidbonnet, a seal between said bonnet and said bonnet cap, and said valvestem seal.
 50. The device of claim 42, further comprising a sealpositioned between said piston and said piston chamber.
 51. The deviceof claim 42, further comprising a hydraulic fluid positioned in saidsealed cavity above said piston, wherein said hydraulic fluid is adaptedto be substantially isolated from said working fluid by said piston. 52.A device, comprising: a body; a bonnet coupled to said body; a valvestem operatively coupled to a gate positioned in said body; a bonnet capcoupled to said bonnet; a roller screw assembly operatively coupled tosaid valve stem, said roller screw assembly comprising a housing, aportion of which extends through said bonnet cap; a first valve stemseal positioned between said valve stem and said bonnet, a second sealpositioned between said bonnet cap and said bonnet, and a third sealpositioned between said bonnet cap and said housing, wherein a sealedcavity exists above said first valve stem seal, said sealed cavity beingdefined by a portion of said bonnet cap, said first valve stem seal,said second seal and said third seal; a piston chamber formed in saidbonnet, said piston chamber being in fluid communication with saidsealed cavity and an interior region of said body; and a pistonpositioned in said piston chamber.
 53. The device of claim 52, furthercomprising a piston retaining ring that is threadingly coupled to saidbonnet, said piston retaining ring being adapted to retain said pistonin said piston chamber.
 54. The device of claim 53, further comprising afilter positioned in said bonnet between said piston and said interiorregion of said body.
 55. The device of claim 53, further comprising: afilter positioned in said bonnet between said piston and said interiorregion of said body; and a filter support ring to retain said filter inposition, said filter support ring being threadingly coupled to saidpiston retaining ring.
 56. The device of claim 52, wherein said valvestem seal is a bi-directional seal.
 57. The device of claim 52, furthercomprising a seal positioned between said piston and said pistonchamber.
 58. The device of claim 52, further comprising a hydraulicfluid positioned in said sealed cavity above said piston, wherein saidhydraulic fluid is adapted to be substantially isolated from saidworking fluid by said piston.
 59. A device adapted to have a workingfluid flow therethrough, said device comprising: a body; a bonnetcoupled to said body; a valve stem operatively coupled to a gatepositioned in said body; a valve stem seal positioned between said valvestem and said bonnet, wherein a sealed cavity exists above said valvestem seal; and means for allowing a pressure of said working fluid to beexerted in said sealed cavity while preventing said working fluid fromentering said sealed cavity.
 60. The device of claim 59, wherein saidmeans comprises a piston positioned in a piston chamber formed in saidbody, said piston chamber being in fluid communication with said sealedcavity and an interior region of said body.
 61. The device of claim 59,wherein said means comprises an opening through said valve body that isin fluid communication with said sealed cavity and an interior region ofsaid body.
 62. The device of claim 59, further comprising a roller screwoperatively coupled to said valve stem.
 63. The device of claim 60,further comprising a filter positioned in a recess in said bonnetupstream of said piston.
 64. The device of claim 60, further comprisinga piston retaining ring that is threadingly coupled to said bonnet. 65.The device of claim 63, further comprising a filter support ring toretain said filter.